dialect/sql/sqljson: add ValueIsNotNull predicate (#3058)

* dialect/sql: add json ValueIsNotNull predicate

* get rid of false positive dupl linter warning

* add json valueIsNotNull case to integration tests

* fix rejects

dialect/sql/sqljson/sqljson.go

@@ -62,6 +62,31 @@ func ValueIsNull(column string, opts ...Option) *sql.Predicate {
 	})
 }
 
+// ValueIsNotNull return a predicate for checking that a JSON value
+// (returned by the path) is not null literal (JSON "null").
+//
+//	sqljson.ValueIsNotNull("a", sqljson.Path("b"))
+func ValueIsNotNull(column string, opts ...Option) *sql.Predicate {
+	return sql.P(func(b *sql.Builder) {
+		switch b.Dialect() {
+		case dialect.Postgres:
+			valuePath(b, column, append(opts, Cast("jsonb"))...)
+			b.WriteOp(sql.OpNEQ).WriteString("'null'::jsonb")
+		case dialect.SQLite:
+			path := identPath(column, opts...)
+			path.mysqlFunc("JSON_TYPE", b)
+			b.WriteOp(sql.OpNEQ).WriteString("'null'")
+		case dialect.MySQL:
+			path := identPath(column, opts...)
+			b.WriteString("NOT(JSON_CONTAINS").Wrap(func(b *sql.Builder) {
+				b.Ident(column).Comma()
+				b.WriteString("'null'").Comma()
+				path.mysqlPath(b)
+			}).WriteString(")")
+		}
+	})
+}
+
 // ValueEQ return a predicate for checking that a JSON value
 // (returned by the path) is equal to the given argument.
 //

dialect/sql/sqljson/sqljson_test.go

@@ -256,6 +256,27 @@ func TestWritePath(t *testing.T) {
 				Where(sqljson.ValueIsNull("c", sqljson.Path("a"))),
 			wantQuery: "SELECT * FROM `users` WHERE JSON_TYPE(`c`, '$.a') = 'null'",
 		},
+		{
+			input: sql.Dialect(dialect.Postgres).
+				Select("*").
+				From(sql.Table("users")).
+				Where(sqljson.ValueIsNotNull("c", sqljson.Path("a"))),
+			wantQuery: `SELECT * FROM "users" WHERE ("c"->'a')::jsonb <> 'null'::jsonb`,
+		},
+		{
+			input: sql.Dialect(dialect.MySQL).
+				Select("*").
+				From(sql.Table("users")).
+				Where(sqljson.ValueIsNotNull("c", sqljson.Path("a"))),
+			wantQuery: "SELECT * FROM `users` WHERE NOT(JSON_CONTAINS(`c`, 'null', '$.a'))",
+		},
+		{
+			input: sql.Dialect(dialect.SQLite).
+				Select("*").
+				From(sql.Table("users")).
+				Where(sqljson.ValueIsNotNull("c", sqljson.Path("a"))),
+			wantQuery: "SELECT * FROM `users` WHERE JSON_TYPE(`c`, '$.a') <> 'null'",
+		},
 		{
 			input: sql.Dialect(dialect.Postgres).
 				Select("*").